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Quantitation of Motion Perception in the Digits: a Psychophysical Study in Normal Human Subjects Emre Kokmen, MD, Robert W

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Quantitation of Motion Perception in the Digits: a Psychophysical Study in Normal Human Subjects Emre Kokmen, MD, Robert W Quantitation of Motion Perception in the Digits: A Psychophysical Study in Normal Human Subjects Emre Kokmen, MD, Robert W. Bossemeyer, Jr, MScEE, and William J. Williams, PhD Threshold perception of motion of the digits was obtained in 14 normal subjects. The metacarpophalangeal joint of the index and the fifth finger of each hand and the metatarsophalangeal joint of the hallux of each foot were passively moved up and down with respect to a horizontal plane defined by the palmar or plantar surface. The motion was sinusoidal at frequencies of 0.5 and 5.0 Hz. A modified von Bekesy paradigm similar to that used in audiometry was utilized to yield threshold levels of motion sensation. There was little difference in the thresholds obtained for the different joints. The difference between high- and low-frequency stimulation, however, was significant (p < 0.001): the 0.5 Hz threshold was found to range from 0.8 to 1 .0 degree, whereas the 5.0 Hz threshold varied from 0.4 to 0.6 degree. It is thought that motion sense is largely dependent on joint receptor contributions, but muscle and cutaneous receptors may also contribute to this proprioceptive sensation. Kokmen E, Bossemeyer RW Jr, Williams WJ. Quantitation of motion perception in the digits: a psychophysical study in normal human subjects. Ann Neurol 2:279-284, 1977 A number of efforts have been made in the past to studying the nature of proprioceptive sensations in quantitate somatic senses [5], including a few studies humans. Such a method can also be a useful tool in the which have attempted to measure perception of mo- longitudinal and comparative evaluation of patients tion of limbs or digits. In 1889 Goldscheider [8] with selected neurological conditions as well as in recorded perception of passive motion in several assessing sensory performance of selected popula- joints moved with an elaborate hydraulic system. tions, such as the aged versus the young. However, Laidlaw and Hamilton [14] moved joints passively before the method can be used in clinical studies, with a hand-cranked mechanical device. Browne, Lee, some normative values must be established. We re- and Ring [2] moved the metatarsophalangeal joint port the motion perception thresholds obtained in a (MTP) passively with a motor-driven assembly. The group of young, healthy naive subjects. subjects indicated perception by depressing a switch, causing the angle through which the digit had been Methods and Materials An electrically controlled mechanical system was developed moved to be recorded. Provins [20] used a similar to move the fingers and toes up and down and to articulate method to study the appreciation of index finger the MCP joint of the index and fifth finger of each hand and movements at the metacarpophalangeal (MCP) joint. the MTP joint of the hallux of each foot. In all cases, the A quantitative psychophysical evaluation is needed subject was completely relaxed and the movement of the to study the characteristics of motion perception in digit was passive. The finger or toe was placed in a padded humans. Bedside clinical sensory testing methods lack plastic clamp that held the digit firmly and prevented motion precise control of stimulation delivery and response of the distal interphalangeal joint. Since we were concerned recording and evaluation. The intensity, frequency, at the outset that differential pressures on the dorsal or direction, and sites of application of the stimuli must ventral surface of the digit might give motion clues, several be controlled, and responses of the subjects must be types of finger and toe holders, including one with an inflat- recorded consistently. able inner liner, were tried in preliminary experiments. The final model used in this study applied uniform pressure to We have devised a minicomputer-assisted method the digit on all sides viaan intermediate liner fabricated from of assessing perception of passive sinusoidal motion of a silicon gel material. the MCP and MTP joints in man, utilizing a modified A minicomputer was programmed to run the experiment von Bekksy procedure similar to that used in au- as well as to record and sort data. An identifyingnumber; the diometry [22]. We believe that a reliable and precise subject’sage, sex, and handedness; the joint to be tested; the quantitation technique is necessary as a first step in date; and the number of trials used were entered by tele- From the Departments of Neurology and of Electrical and Com- ALcepted for publication May 20, 1977. puter Engineering, University of Michigan Medical Center, Ann Arbor, MI. Address reprint requests to Dr Kokmen, University of Michigan Medical Center, Ann Arbor, MI 48 109. 279 typewriter and stored in computer disc files. The threshold sensation. The subject was instructed to release the finger stimulus intensity in degrees, the frequency of stimulation, from the switch when the sensation of movement was lost, and summary statistics concerning the response of the sub- and the amplitude of the stimulus was then increased once jects were also stored in the disc file. A block diagram of the more. In this way, it was possible to obtain a series of upper system is shown in Figure 1. and lower thresholds of sensation of movement for each Fourteen normal test subjects, 6 women and 8 men, were digit, This is similar to von BikPsy’s audiometric method recruited from co-workers, acquaintances, and students. [22]. The actual threshold was assumed to be the level of The age range was from 18 to 29 years with a median of 23 stimulus intensity above which the subject detected move- and a mean of 22.2 years. Thirteen subjects were right- ment more than 50% of the time. Precise measurement of handed and 1 was left-handed. This was the first testing of the stimulus intensity was accomplished electronically and this type for each of the subjects; personnel who had been recorded by the computer whenever the subject responded involved in the development of the apparatus and had tested by moving his finger to or from the switch. and retested themselves were excluded from the study To acquaint the subject with the testing procedure and group. the sensations he might be experiencing, a trial test on the The subjects were seated comfortably in a dimly lit room. right index finger was carried out before data gathering was They extended their extremity to be tested into the ap- begun. At the end of the trial test, another conversation paratus (Fig 2). A cloth drape was positioned over the hand session was held with the subject to answer questions or or foot to exclude vision. The digit to be tested was isolated clarify points. The results of this trial test were not included from the others by gently applied cloth straps, and the in the final data reported. extremity was supported (Fig 2, inset). A standardized para- For each digit tested, seven pairs of threshold estimates graph stating the goals and procedures of the experiment were obtained at test frequencies of 0.5 and 5.0 Hz. The first was read aloud, and the subject was given the opportunity to two pairs were discarded to reduce or eliminate carryover ask questions before testing was begun. from a previous test frequency, and the remaining five The joint to be tested was passively flexed and extended measurements were used for all calculations. The testing in a sinusoidal fashion; these sinusoidal stimuli were varied time was approximately 15 minutes for each digit tested, in intensity and frequency. The digit to be tested was on the thus requiring approximately 90 minutes for the completion same plane as the palmar surface of the hand or the plantar of an experiment for a given subject. This included surface of the foot at the beginning of the experiment. For a changeover time between digits. given frequency, the stimulus intensity gradually increased from zero to a maximum of 10 degrees of total motion of the Results joint. The sinusoid stimulus was applied continuously and The Table gives a sample listing of the data from one was slowly increased in intensity until perceived by the digit, including the mean value of upper, lower, and subject. The subjects were instructed to concentratc on a actual thresholds as well as the standard deviations for sense of motion of the digit and were asked to indicate the each frequency tested. A coefficient of variation ob- earliest perception of movement by placing a finger of tained by multiplying the standard deviation by 100 the other hand on a specially designed response switch. and dividing the result by the mean is also shown. A When the subject indicated perception of movement by listing each data point is also included. pressing the response switch, the stimulus amplitude was of gradually decreased until it was below the threshold for Fig 1. Diagram of the testing and recording apparatus. TELETYPE WRITER SYSTEM PRINTER DATA PROCESSING DATA OUTPUT AND STORAGE DIGITAL POSITION MECHANICAL ACTUATOR SERVO CONTROLLER SUBJECT AND CONTROLLED UNDER . COMPUTER BY THE TEST RESPONSE INTERFACE SERVO SYSTEM SWITCH CIRCUITS A i 280 Annals of Neurology Vol 2 No 4 October 1977 Fig 2.1 ‘be te.rting apparatus, .rhowing nreihmiral assembly. Inset shoico subject? irrdex.frnger in place. Sample of Azuzlable Computer Data jw Each Dtgit ‘Ierted Female 22 years hght-handed Right index finger Upper Threshold Lower Threshold Threshold Frequency M SI) cv M SD cv M SD cv 0.5 1.05 0.07 6.67 0.52 0.06 11.54 0.70 0.05 6.33 5.0 0.54 0.04 7.40 0.35 0.03 8.57 0.45 0.02 4.44 Individual data points for the above means for upper and lower thresholds: Frequency = 0.5 Hz Response No.
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